A. Technical Field
The present invention relates to a production process for a hydroxyalkyl(meth)acrylate, which comprises the step of carrying out a reaction between (meth)acrylic acid and an alkylene oxide.
B. Background Art
As to production processes for a hydroxyalkyl(meth)acrylate which comprises the step of carrying out a reaction between (meth)acrylic acid and an alkylene oxide, it is known that the alkylene oxide is supplied to a reactor in a molar quantity excessive to (meth)acrylic acid so that the formation of by-products can be inhibited, and that the conversion can be enhanced as much as possible (e.g. JP-B-013019/1966, JP-B-018890/1968). In this case, the unreacted residue of the alkylene oxide is present in the resultant reaction liquid at the end of the reaction. Therefore, after being separated from the reaction liquid, this residue needs to be disposed of, or recovered and recycled.
In the case where the unreacted residue of the alkylene oxide is stripped by vaporization under reduced pressure in order to separate it from the reaction liquid, the stripping efficiency would be bad without the reaction liquid being put under high vacuum, because the alkylene oxide much dissolves into the reaction liquid. Therefore, a high cost is needed for vacuum facilities which are used to achieve high vacuum. In addition, under reduced pressure, the reaction liquid undergoes asphyxiation polymerization because oxygen dissolved in the reaction liquid is deaerated.
On the other hand, the recovering and recycling is economically advantageous. However, in the case where the unreacted residue of the alkylene oxide is stripped by vaporization under reduced pressure, a refrigerant having an extremely low temperature is necessary for the condensation of the vaporized alkylene oxide gas by use of the refrigerant under reduced pressure, therefore the resultant process cost is high.
Thus, if the alkylene oxide gas as vaporized under reduced pressure is condensed by compression to not lower than normal pressure with a compressor, then the temperature of the refrigerant can be set to be high. However, when the alkylene oxide gas is adiabatically compressed, the gas temperature rises to enlarge a danger of explosion.
In addition, JP-A-330320/1998 discloses that the unreacted alkylene oxide residue can be effectively utilized by causing it to be absorbed into raw (meth)acrylic acid and then recycling this (meth)acrylic acid containing the ethylene oxide for the addition reaction. However, in respect to the recovery efficiency, this prior art cannot be said to be on a sufficiently satisfactory level.
A. Object of the Invention
An object of the present invention is to provide a production process for a hydroxyalkyl(meth)acrylate which comprises the steps of carrying out a reaction between (meth)acrylic acid and an alkylene oxide and stripping the unreacted residue of the alkylene oxide from the resultant reaction liquid, wherein the production process enables to safely and efficiently strip the unreacted residue of the alkylene oxide, or enables to economically and efficiently recover and recycle the unreacted residue of the alkylene oxide.
B. Disclosure of the Invention
The present inventors diligently studied to solve the above-mentioned problems. As a result, the inventors hit on an idea that: if (1) an inert gas having a specific composition is used as a stripping means, then there is no danger of explosion, and the possibility of the asphyxiation polymerization in a stripping apparatus can be lessened. Furthermore, the inventors found that: also if (2) the concentration of the unreacted residue of the (meth)acrylic acid in the resultant reaction liquid is suppressed to not more than a specific value, then the effects of the present invention are sufficiently exhibited.
In addition, the inventors further hit on an idea that: in the case where the production process further comprises the step of causing the unreacted residue of the alkylene oxide to be absorbed after the step of stripping the unreacted residue of the alkylene oxide from the resultant reaction liquid, if (3) the difference in operational pressure between the steps of stripping the unreacted residue of the alkylene oxide from the resultant reaction liquid and causing the stripped alkylene oxide to be absorbed is suppressed to not more than a specific value, then both the stripping efficiency and the absorption efficiency can be maintained on a practical use level, while the danger of explosion of the unreacted alkylene oxide residue can be avoided.
In addition, it is generally preferable, for enhancing the stripping efficiency, that the temperature of the reaction liquid is high when the reaction liquid is introduced into the stripping step. However, for example, in the case where the reaction liquid containing the unreacted residue of the alkylene oxide is subjected to a heating operation before being introduced into the stripping step, there are disadvantages in that there is a great danger of explosion. Thus, the inventors studied to seek a process that can enhance the stripping efficiency even if the reaction liquid is not heated before the stripping step. As a result, the inventors hit on the following two ideas.
Namely, the inventors hit on an idea that: if (4) the reaction liquid resultant from the reaction is directly supplied to the stripping step without being heated, then the stripping efficiency is enhanced due to sensible heat of the reaction liquid, and further, there is no danger of explosion. In addition, the inventors further hit on an idea that: if (5) a part of the liquid left behind in the stripping step is heated and then supplied to the stripping step again, the stripping temperature in the stripping step can be raised without raising the temperature of the reaction liquid as introduced into the stripping step, so the stripping efficiency can be enhanced without a danger of explosion.
Furthermore, the inventors directed their attention to a fact that, in the case of the mode further comprising the absorption step after the stripping step, the lower the temperature of the absorbing solvent becomes, the higher the absorption efficiency of the alkylene oxide becomes, and then the inventors considered that: (A) the lower the solidifying point of the absorbing solvent is, the more the cooling temperature can be lowered; and (B) the temperature of the solvent rises due to absorption of alkylene oxide vapor, therefore if the temperature rise of the solvent involved by this absorption can be suppressed the absorption efficiency is also enhanced. Then, from the above point (A), the inventors found that: if (6) a hydroxyalkyl(meth)acrylate of which the solidifying point (about xe2x88x9270xc2x0 C.) is much lower than that (about 15xc2x0 C.) of (meth)acrylic acid is used as the absorbing solvent, then the absorbing solvent can be cooled to a fairly low temperature, and further, the alkylene oxide can be recovered and recycled with a high efficiency. In addition, from the above point (B), the inventors found that: if (7) a part of the liquid resultant from the absorption step is cooled and then supplied to the absorption step again, or if (8) a part or the whole of the absorbing liquid which is on the way of the absorption step is extracted and then cooled and then supplied to the absorption step again, the temperature rise of the absorbing solvent can efficiently be suppressed.
The present invention has been completed in the above way.
That is to say, a production process for a hydroxyalkyl(meth)acrylate, according to the present invention, comprises the steps of carrying out a reaction between (meth)acrylic acid and an alkylene oxide and stripping the unreacted residue of the alkylene oxide from the resultant reaction liquid, with the production process being characterized in that the stripping step is performed by use of an inert gas, and in that the concentration of oxygen in the inert gas is adjusted in the range of 0.1 to 5 mol %.
Another production process for a hydroxyalkyl(meth)acrylate, according to the present invention, comprises the steps of carrying out a reaction between (meth)acrylic acid and an alkylene oxide and stripping the unreacted residue of the alkylene oxide from the resultant reaction liquid, with the production process being characterized in that the concentration of the unreacted residue of the (meth)acrylic acid in the resultant reaction liquid is suppressed to not higher than 10 weight %.
Yet another production process for a hydroxyalkyl(meth)acrylate, according to the present invention, comprises the steps of: carrying out a reaction between (meth)acrylic acid and an alkylene oxide; stripping the unreacted residue of the alkylene oxide from the resultant reaction liquid; and causing a solvent to absorb the stripped alkylene oxide; with the production process being characterized in that the difference in operational pressure between the stripping step and the absorption step is not more than 1,000 hPa.
Yet another production process for a hydroxyalkyl(meth)acrylate, according to the present invention, comprises the steps of carrying out a reaction between (meth)acrylic acid and an alkylene oxide and stripping the unreacted residue of the alkylene oxide from the resultant reaction liquid, with the production process being characterized in that the reaction liquid resultant from the reaction is directly supplied to the stripping step without being heated.
Yet another production process for a hydroxyalkyl(meth)acrylate, according to the present invention, comprises the steps of carrying out a reaction between (meth)acrylic acid and an alkylene oxide and stripping the unreacted residue of the alkylene oxide from the resultant reaction liquid, with the production process being characterized in that a part of the liquid left behind in the stripping step is heated and then supplied to the stripping step again.
Yet another production process for a hydroxyalkyl(meth)acrylate, according to the present invention, comprises the steps of: carrying out a reaction between (meth)acrylic acid and an alkylene oxide; stripping the unreacted residue of the alkylene oxide from the resultant reaction liquid; and causing a solvent to absorb the stripped alkylene oxide; with the production process being characterized in that a hydroxyalkyl(meth)acrylate solution is used as the absorbing solvent.
Yet another production process for a hydroxyalkyl(meth)acrylate, according to the present invention, comprises the steps of: carrying out a reaction between (meth)acrylic acid and an alkylene oxide; stripping the unreacted residue of the alkylene oxide from the resultant reaction liquid; and causing a solvent to absorb the stripped alkylene oxide; with the production process being characterized in that a part of the liquid resultant from the absorption step is cooled and then supplied to the absorption step again.
Yet another production process for a hydroxyalkyl(meth)acrylate, according to the present invention, comprises the steps of: carrying out a reaction between (meth)acrylic acid and an alkylene oxide; stripping the unreacted residue of the alkylene oxide from the resultant reaction liquid; and causing a solvent to absorb the stripped alkylene oxide; with the production process being characterized in that a part or the whole of the absorbing liquid which is on the way of the absorption step is extracted and then cooled and then supplied to the absorption step again.
These and other objects and the advantages of the present invention will be more fully apparent from the following detailed disclosure.